drm/i915/dp: Add missing slice count check during mode validation

Add the missing check for a valid slice count during
mode validation when DSC is enabled.

Cc: Vinod Govindapillai <vinod.govindapillai@intel.com>
Fixes: 745395b ("drm/i915/dp: Add intel_dp_mode_valid_with_dsc()")
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260216070421.714884-2-imre.deak@intel.com
(cherry picked from commit ec4db42)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Author: ideak

drivers/gpu/drm/i915/display/intel_dp.c

@@ -2557,6 +2557,9 @@ bool intel_dp_mode_valid_with_dsc(struct intel_connector *connector,
 	if (min_bpp_x16 <= 0 || min_bpp_x16 > max_bpp_x16)
 		return false;
 
+	if (dsc_slice_count == 0)
+		return false;
+
 	return is_bw_sufficient_for_dsc_config(intel_dp,
 					       link_clock, lane_count,
 					       mode_clock, mode_hdisplay,